1. Field of the Invention
This invention relates to diaphragm aperture exposure servo-control devices for cameras, and in particular to such devices incorporating damping for preventing transient effects caused by diaphragm overshoot.
2. Prior Art
Known exposure servo-control devices control the diaphragm aperture by driving the diaphragm blades in association with the movement of the movable coil or magnet of an ammeter responsive to the output of a photosensitive element. In such an exposure servo-control device, however, when the brightness of the object to be photographed suddenly changes immediately before exposure, the inertial force of the movable element including the movable coil or magnet results in an overshoot of the diaphragm and produces the so-called transient effect. Such a transient effect presents a serious problem particularly in the case of cinematographic cameras. To prevent such an overshoot, it has been proposed, for instance, to incorporate a feedback or damping coil in juxtaposition with a driving coil in the exposure servo-control device to ensure an appropriate damping characteristic. Such damping coil devices are disclosed in U.S. Pat. Nos. 3,747,487 and 3,896,461. But such an arrangement has the disadvantage of complicated construction and high production cost.